The present invention relates to a semiconductor switching device, and its control circuitry for controllably supplying high voltage power to an electric load. More particularly, the invention relates to a power interface circuit in which low voltage control circuitry is located off the power chip but is powered from a voltage regulator contained within the power chip.
Conventional power interface circuits ("PIC's") are useful for applying high voltage power to an electrical load in a controllable manner. Such PIC's are shown in pending application Ser. No. 555,025, filed Nov. 25, 1983, and in pending application Ser. No. 581,785, filed Feb. 21, 1984, each assigned to the assignee of the present invention. These devices are commercially marketed under the trade names "ChipSwitch" and "PVR" respectively, by the assignee of the present application.
Power interface circuits include a control terminal, such as the "gate" of a thyristor, or the "base" of a power bipolar transistor. Control circuits of various forms have been proposed to provide switching signals on the control terminals of switching devices. The control circuits may also provide various forms of power conditioning, such as increasing the duty cycle of supplied power from no load to full load in a gradual manner, controlling zero cross firing, suppressing firing due to voltage surges and the like.
A conventional approach to implementing a PIC has been to integrate both a power switching structure and its associated control circuitry in the same chip body. PIC devices of this sort are sometimes referred to as "smart" power IC's, due to the inclusion of often sophisticated control circuitry in the power chip.
At the present time the amount of intelligence that can be integrated into one power device is limited for reasons to be stated hereinafter. This invention provides a technique whereby a significant amount of intelligence can be incorporated into a PIC by means of well established and inexpensive methods.
The voltage withstanding capability of a power switch, integrated or not, is one of its most important features. This is particularly true in noisy environments, such as encountered in industrial and automotive applications, where voltage transients are quite common. In a monolithic PIC all the intelligence and control functions either must have the same voltage withstanding capability as the power switching unit, or else special buffering and isolation techniques must be used to effectively shield such control functions from the high voltage part of the die. These techniques increase the die size and processing costs.
Since this withstanding voltage is normally greater than 30 or 40V, the traditional, well established and inexpensive manufacturing techniques that are normally employed to build circuits and microprocessors cannot be used for an "intelligent" PIC. Other fabrication techniques have to be used which require large amounts of silicon die area to integrate the most basic functions. These techniques have an intrinsically low yield. This, in turn limits the amount of intelligence that can be made part of the power switch.